1. Field of Invention
The present invention relates to an electro-optical circuit board, and more particularly, to an electro-optical circuit board having an optical waveguide supporting structure.
2. Related Art
With the development of Internet, people's demanding on the bandwidth of the network is increasingly high, and the optical network has gradually developed towards the trend of large volume, variable changes, high reliability, and cost efficiency. The optical communication has been developed from the backbone network, the metropolitan network, the access network, the storing network towards completely achieving the optical fiber, and furthermore, the optical networking has been achieved step by step, and the fiber to the home (FTTH) has been gradually established. The bottleneck of the bandwidth lies in the so-called “the last one meter”, which includes the following three fields, Rack to Rack, Board to Board, and Chip to Chip.
Currently, the short distance interconnection technology is still mainly achieved by copper leads. As the development of the VLSI technology, IC is capable of processing the more complex science and technology analysis and calculation, and achieving the high performance network system, which promotes the FTTH wideband service. The volume of the IC is increasingly reduced, which is suitable for achieving the products of mobile phone, PDA, hand-held computer, so as to bring more convenience and fun in using. In the past two decades, the operating frequency of the microprocessor has gradually increased, and the trend still goes on in the future. The forecasting of the International Technology Roadmap for Semiconductor (ITRS) shows that, the frequency of the microprocessor reaches up to 10 GHz in 2011, but it is not easy for the IC to achieve a high frequency connection to the external device. Nowadays, the electrically interconnection of the chip is constructed on the printed circuit board (PCB), on the electrical switching joint, via holes, and branches, and the discontinuous impedance causes the attenuation and the distortion of the signal, and even worse, the transmitting distance is influenced.
The conventional electrical connecting performance is greatly limited by the signal attenuation, the electromagnetic radiation and interference. In order to overcome the above problems, the optical interconnection may be used to achieve the high bandwidth and high performance data transmission, since it has the advantages of without causing the problem of electromagnetic radiation and without being interfered by the electromagnetic radiation to generate noises. The optical method is used to connect the computer chip, the circuit board, the backboard, the host, and the processor, the high speed photon method is used to transmit signals, so as to solve the bottleneck problem of heating, speed, and limited bandwidth during the conventional electronic transmission.
In US Publication Patent U.S. Pat. No. 6,804,423, entitled “OPTICAL/ELECTRICAL WIRING MOUNTED BOARD AND METHOD OF MANUFACTURING OPTICAL-ELECTRICAL WIRING BOARD”, an electro-optical lead substrate is provided. Referring to FIGS. 1 and 2, FIG. 1 is a top view of a conventional electro-optical circuit board 10, and FIG. 2 is a cross-sectional side view of the conventional electro-optical circuit board 10 in FIG. 1 obtained along a 2-2 sectional line. As shown in FIGS. 1 and 2, the conventional electro-optical circuit board 10 includes an optical guiding layer 12 and an electrical wiring board 14 formed on the optical guiding layer. The optical guiding layer 12 includes a core to serve as the optical waveguide, which is formed by a horizontal optical waveguide 20 and a vertical optical waveguide 22, so as to transmit high frequency optical signals. The electrical wiring board 14 has a through-hole to accommodate the vertical optical waveguide 22. Moreover, the optical guiding layer 12 further includes a horizontal clad 30 formed around the horizontal optical waveguide 20 to make the horizontal optical waveguide 20 buried therein, and a vertical clad 32 formed around the vertical optical waveguide 22 to make the vertical optical waveguide 22 be buried therein. Furthermore, four optical pads 52, 54, 56, and 58 are formed on the surface of the electrical wiring board 14, so as to make the optical guiding layer 12 be electrically interconnected to the electrical wiring board 14.
In addition, a reflecting mirror 40 is further disposed in the optical guiding layer 12, and disposed between the horizontal optical waveguide 20 and the vertical optical waveguide 22 by way of forming an angle of 45 degrees with the horizontal optical waveguide 20 and the vertical optical waveguide 22 respectively. The horizontal clad 30 and the vertical clad 32 are fabricated by the material with the index of refraction lower than that of the core, so the optical signals are sent from the optical element (not shown), and then, enter into the horizontal optical waveguide 20 and then reflected to the vertical optical waveguide 22 through the reflecting mirror 40, so as to achieve the excellent optical signal transmission.
The advantage of the above construction is that, the optical waveguide is integrated with the circuit board, and it is easy to join the optical element with the optical waveguide and the circuit board, so as to fabricate an electro-optical circuit board capable of transmitting optical signals and electrical signals. However, the circuit board is joined with the optical guiding layer through the laminating process, which is a high-temperature and high-pressure process. The optical waveguide is fabricated by the polymer material, and it is easily deformed in the high temperature and the high pressure, and the transition temperature of the optical waveguide is only about 180° C. In the laminating process with high temperature and high pressure, the optical path of the whole optical waveguide is offset, and even if it returns to the normal temperature and normal pressure, it is impossible to return to the expected optical coupling efficiency, so as to result in the great loss of the optical signal. Referring to FIG. 3, it is a curve diagram of the mirror angle and optical coupling efficiency of the conventional optical waveguide. As shown in FIG. 3, in the laminating process, when the reflecting mirror of the optical waveguide deforms from 45 degrees to 38 degrees, the optical coupling efficiency is reduced form 83% to 39%.
Therefore, it is an urgent problem to be solved in this field that how to successfully join the optical waveguide with weak structure with the circuit board without affecting the laminating process of the conventional PCB, so as to not affect the properties of the optical waveguide.